Studies on the generation of enolate anions from butane-2,3-diacetal protected glycolic acid derivatives and subsequent highly diastereoselective coupling reactions with aldehydes and acid chlorides
作者:Steven V. Ley、Darren J. Dixon、Richard T. Guy、Maria A. Palomero、Alessandra Polara、Félix Rodríguez、Tom D. Sheppard
DOI:10.1039/b412790k
日期:——
Highly diastereoselective coupling reactions of enolates derived from butane-2,3-diacetal protected glycolic acids 1 and 2 and their alkylated derivatives with aldehydes are reported together with their efficient acid-catalysed deprotection to yield enantiopure anti-2,3-dihydroxyesters. A procedure to provide the corresponding syn-2,3-dihydroxyesters is also described in two cases, proceeding via an acylation–reduction sequence. An usual double addition reaction of butane-2,3-diacetal protected glycolic acid to small aliphatic acid chlorides provides a synthetically useful, densely-functionalised lactone after acidic deprotection.
The catalytic osmylation of electron-poor allylic ethers and alcohols was studied. In the case of γ-alkoxy E-enoates reaction selectivity was found to range from 2:1 to 8:1 in favor of the arabino (2,3-syn - 3,4-anti) product, regardless of the double bond substitution. Lower (if any) selectivity was found for the Z-isomers. On the contrary, 2-Mthylene-3-hydroxy esters were osmylated with virtually
Highly Diastereoselective Lithium Enolate Aldol Reactions of Butane-2,3-diacetal Desymmetrized Glycolic Acid and Deprotection to Enantiopure <i>anti</i>-2,3-Dihydroxy Esters
作者:Darren J. Dixon、Steven V. Ley、Alessandra Polara、Tom Sheppard
DOI:10.1021/ol016707n
日期:2001.11.1
[reaction--see text] The butane-2,3-diacetal (BDA) desymmetrized glycolic acid building block 1 undergoes efficient and highlydiastereoselective lithium enolate aldol reactions with both aromatic and aliphatic aldehydes to afford, after an acidic methanolysis deprotection step, the enantiopure anti-2,3-dihydroxy esters in good yield.